CN113853489A

CN113853489A - Expander unit for a drum brake of a motor vehicle

Info

Publication number: CN113853489A
Application number: CN202080035230.5A
Authority: CN
Inventors: M·格德克; H·冯海因; M·舒利茨; A·塞弗; U·巴赫; A·梅斯纳; W·里特尔; J·霍夫曼; C·维
Original assignee: Continental Teves AG and Co OHG
Current assignee: Continental Automotive Technologies GmbH
Priority date: 2019-06-05
Filing date: 2020-05-27
Publication date: 2021-12-28
Also published as: DE102019208223A1; WO2020244991A1; EP3980657A1; EP3980657B1; US20220333657A1

Abstract

The invention relates to a spreader unit (2) for a drum brake (1) having an adjustment device (26) which ensures that the clearance remains substantially constant even in the event of wear of the brake lining (5). The adjusting device (26) is designed in such a way that, in the event of an increase in the actuation travel of the expander unit (2) due to wear, the claw of the claw clutch is rotated by one notch further, so that the expander unit does not retract completely when the brake is released. The original gap is thereby maintained. However, an increase in the actuation travel of the expander unit also occurs when the brake, in particular the brake drum, heats up and thus expands in the event of prolonged braking. In this case, however, no adjustment should occur. Thus, a blocking device is provided, which consists of a bimetallic element, for example in the form of a helical spring (53). Upon heating, the blocking means expand and keep the two pawls (19, 27) of the dog clutch spaced apart, so that they do not fall into the next recess despite the increase in actuation travel. The adjustment is thus intentionally prevented. The wear on the lining is compensated in one of the subsequent braking operations in which the brake does not generate significant heat.

Description

Expander unit for a drum brake of a motor vehicle

Technical Field

The invention relates to an expander unit, in particular electromechanically drivable, for a drum brake of a motor vehicle, comprising a housing and two first and second brake shoe holders, which are arranged in a rotationally fixed manner and are fastened relative to the housing, can be actuated linearly along an axis respectively away from one another in an expansion direction and respectively towards one another in a release direction, and act respectively on a first brake shoe and a second brake shoe provided with brake linings respectively, wherein the linear movement of the brake shoe holders is generated by one or more rotation-translation conversion devices, and wherein, between the actuating pistons, readjustment means are arranged for compensating an increased actuating stroke due to brake lining wear, which readjustment means are designed such that, when the actuating stroke exceeds a set value, the readjustment device changes the pitch of the actuating piston in at least one readjustment step.

Background

A dilator unit is described in german co-pending application DE 102017218219 a 1. The readjustment device has the purpose of compensating the wear on the brake lining so that the spacing (i.e. the clearance) between the lining and the brake drum remains substantially the same regardless of the state of wear of the lining, so that the expander unit always has to perform the same actuation stroke to actuate the brake.

In the case of long braking, for example on downhill stretches, the brakes develop a significant heating, wherein the brake drum expands, so that the expander unit has to perform a longer actuation stroke than the cold (contracting) drum state for the purpose of automatically compensating the stroke or for the purpose of maintaining the braking effect. This compensation results in readjustment even if there is no corresponding wear. After cooling of the brake, the clearance is thus correspondingly reduced, without excluding the situation in which the lining sticks to the brake drum or the drum brake is undesirably wedged, i.e. cannot be released. To avoid this, a larger original gap is selected accordingly, but this means a longer actuation stroke. Nevertheless, in order to obtain a fast acting brake, the motor driving the expander unit must respond fast enough and the expander unit must not have too much internal friction. This increases the structural complexity and the energy requirement for braking.

Disclosure of Invention

The invention is therefore based on the object of creating an expander unit which, despite its relatively small size of the original gap, ensures that no sticking/wedging between the friction lining and the brake drum occurs in the event that the brake drum has already undergone a temperature-dependent expansion at the start of braking.

In order to achieve this object, the invention provides a thermally activatable blocking device which is designed to mechanically prevent the readjusting device from performing a readjusting step at a temperature above a set value.

This has the result that, in a currentless automatic manner, when the detected brake temperature is above a predetermined, defined set temperature value, no or fewer readjustment steps are carried out at all for compensation purposes in order to prevent excessive readjustment. Otherwise, due to the temperature-dependent expansion of the brake, the readjusted actuation travel of the expander unit will have dimensions linked to a high degree of wear of the brake pads in the case of cold braking. Since the readjustment step is prevented or adapted, the originally designed (unaffected) clearance is re-established after the braking associated with the brake temperature increase and after the brake cools down. Thus, wear-related readjustment only occurs when the temperature of the brake does not rise above the set temperature value during brake actuation/braking.

Preferably, the readjustment device has a freewheel clutch (freewheel/idle clutch) which comprises two pawls and works in an incremental manner, wherein during idle rotation the pawls perform a relative stroke, and wherein one pawl is connected in a tight but non-rotating manner to the first brake shoe holder and the other pawl is connected by a threaded shaft to the second actuating piston.

When the brake is actuated, the first brake shoe holder rotates relative to the second actuation piston in the direction of the idle rotation of the dog clutch. As long as the angle of rotation remains below the predetermined step width, the freewheel clutch rotates back to its original position when the brake is released. However, if the step width is exceeded during braking, the freewheel clutch remains in the angular position reached when the brake is released, with the result that the second actuating piston is permanently axially offset by the threaded shaft relative to the first actuating piston, wherein this offset compensates for the wear of the brake lining which has thus far been reached.

During the idle rotation, the jaws move away from each other, i.e. perform a relative stroke. This can be used to allow the freewheel clutch to go to its starting position even when the step width is exceeded. For this purpose, the blocking device is operatively arranged parallel to the claw clutch and thus holds the claws apart in the activated state.

Preferably, the claws have on their respective one end face serrated inclined surfaces extending in a circle and engaging each other, wherein the length of the inclined surfaces on the circular arc defines the predetermined step width and the height of the inclined surfaces defines the maximum claw stroke. Each ramp forms a notch such that the dog clutch jumps into the next notch when the step width is reached.

The saw tooth ramps have the effect of preventing the jaws from rotating relative to each other in the circumferential direction and exerting an axial force in the opposite circumferential direction. If in the latter case the two jaws rotate relative to each other, the ramps slide over each other, so that the jaws move apart. Once the actuation stroke of the expander unit becomes too great due to wear, the rotation of the jaws becomes greater than the step width, so that the jaws jump into the next notch. When the brake is released, the claw connected to the first brake shoe holder will be carried along the other claw, so that their rotation is converted by the shaft connection into a translational movement of the second actuation piston. As a result, the two actuating pistons are spaced further apart from each other, thereby reestablishing the original gap.

In the event of significant heating of the brake during the braking operation, the actuation stroke likewise increases in size, but this should not lead to readjustment. The blocking means thus prevent the pawl from engaging in the next recess, and therefore the pawl falls back into the original recess when the brake is released. And therefore no readjustment. This is also undesirable, since the increased actuation travel is not caused by wear of the linings, but rather by temperature-dependent expansion of the brake drum.

Preferably, the blocking means is represented by a bimetal element, wherein between the jaws there is a blocking space laterally delimited by the jaws, and wherein the bimetal element is arranged to be expandable into or in the blocking space at least when a maximum jaw travel is reached.

At the latest when the pawl rotates as a result of the increase in the actuating travel and in the process opens to such an extent that the pawl can jump into the next recess, the bimetal element slides into the blocking space or expands in the blocking space and prevents this from occurring, because the pawl bears on both sides on the bimetal element instead of falling back into the recess.

An embodiment of the bimetal element may consist of a helical spring, the diameter of which varies as a function of temperature and which is arranged such that its outer edge enters the blocking space under temperature-dependent expansion. This helical spring is arranged coaxially with the axis of the expander unit between the two jaws. When the brake heats up, the coil spring expands so that its outer edge enters the blocking space.

Another possibility is that the bimetal element has at least one arm extending from the centre, which at least one arm lengthens depending on the temperature and which at least one arm is arranged such that its distal end enters the blocking space at a temperature-dependent lengthening of the arm.

In order to ensure a uniform spacing of the claws in the circumferential direction, it is of course also possible to arrange a plurality of arms in a star shape.

Another embodiment of the bimetal element comprises two coil springs arranged in opposite directions, one respective side of said two coil springs being convex or concave depending on the temperature, and the outer edges of said two coil springs being located in the blocking space.

In the cold state, the coil springs are arranged such that their facing faces are embodied in a concave manner, so that their outer edges are close together and do not fill the width of the blocking space in the case of non-actuated brakes. If a certain set temperature is reached, the coil spring is turned over so that the mutually facing surfaces are bulged. The outer edge can then bear on the two claws and keep them at a distance which is at least greater than the claw travel.

If desired, a plurality of pairs of coil springs may be arranged in series and may also be held spaced apart by spacer rings.

The rotation-translation conversion component can be configured to present in various combinations of ways. For the purpose of electromechanical actuation, the dilator device according to the invention cooperates with an electric actuator, which can be configured particularly effectively as a motor-transmission unit that can be operated independently or mounted. An expander unit configured according to the invention can have an electronic control unit with an electrical load measuring device for the purpose of cooperation or interaction (i.e. closed-loop or open-loop control of the actuator system) in an electric drum brake system, wherein the load measuring device can in principle be present integrated in any desired position. Accordingly, according to the invention, this may provide an electromechanical motor vehicle drum brake system which is controllable in a wheel-specific manner by open-loop or closed-loop control and comprises at least two drum brakes on a common axle, which drum brakes are configured as service brake system components and can accordingly be under closed-loop control, in particular under remote control. The drum brake/expander device equipped according to the present invention can be positioned in an indirect or direct attached or integrated manner, i.e. in the broadest sense close to the drive train, on both sides of the drive.

The claw clutch is preferably embodied such that the claw connected to the first brake shoe holder is in the form of a locking sleeve which is firmly connected to the first brake shoe holder, and the claw coupled to the second actuating piston is in the form of a readjusting piston, wherein the locking sleeve is fastened against rotation relative to the second brake shoe holder, is axially movable relative to the second actuating piston to a limited extent, and is arranged in an elastically preloaded manner against the readjusting piston.

Drawings

The invention will be explained in more detail below on the basis of four exemplary embodiments. In the drawings:

figure 1 shows a highly simplified cross-sectional view of a drum brake with a simple design of the expander unit according to the invention,

figure 2 shows an embodiment of the expander unit in axial section without the blocking means yet,

fig. 3a, 3b, 3c show enlarged representations of a dilator unit with a first embodiment of a blocking means according to the invention, having a bimetallic coil spring in various stages of brake actuation,

figures 4a and 4b show a star-shaped bimetallic element as a second embodiment of the blocking device according to the invention,

fig. 5a, 5b show a bimetallic element consisting of two coil springs as a third embodiment of the blocking device according to the invention, an

Fig. 6 shows a bimetallic element consisting of two pairs of disc springs as a fourth embodiment of the blocking device according to the invention.

Detailed Description

Since the basic operating modes of both drum brakes and rotation-translation transformation devices (e.g. ball-ramp devices) are sufficiently well known, only those functional characteristics that are essential to the present invention will be explored below.

Fig. 1 shows, by way of example and in highly simplified form, a generic drum brake 1 of simple design. However, other known designs of drum brakes are equally applicable to the present invention. The two substantially circular-arc-shaped brake shoes 4, 4 ' are each rotatably supported at their first ends 13, 13 ', are each separated at their second ends 12, 12 ' by the expander unit 2, and are in the process pressed against the radially inner wall 7 of the pot brake drum 6. The brake drum 6 is connected to a wheel (not shown) and rotates together with the wheel relative to the brake shoes 4, 4'. In the process, the brake linings 5, 5 'attached to the brake shoes 4, 4' rub against the inner wall 7. As a result of the wear of the brake linings 5, 5', the expansion travel required for the braking process increases until a defined wear limit is reached. In order to compensate for any asymmetrical, uneven contact between the linings 5, 5' and the brake drum 6, the expander unit 2 is arranged in the drum brake in such a way as to float, preferably along its central axis a.

Fig. 2 shows an embodiment of the expander unit 2 according to the invention in an unactuated initial state in axial section. The expander unit 2 has two ball ramp arrangements 3, 3 ' which act on the brake shoes 4, 4 ' by means of brake shoe holders 31, 31 '. For this purpose, each brake shoe holder 31, 31 'has a transverse groove 36, 36' in which the flat end 12, 12 'of the brake shoe 4, 4' is arranged. The expander unit 2 also has a generally tubular housing 14 equipped with a mounting flange. The expander unit 2 is driven by an electric motor drive unit 8 shown in fig. 1 via external teeth 10 of a drive sleeve 9, which is thus rotated about an axis a and supported in a housing 14 by rolling bearings 15, 15 'and axially fixed by fastening elements 16, 16'. Since the drum brake 1 according to the invention is provided as a service brake, all braking processes, not just static, constant force application, for example during parking, are initiated by the drive sleeve 9.

In the embodiment shown, the rolling bearings 15, 15' are in the form of needle bearings, but other types of rolling bearings are equally permissible within the invention. The braking process takes place by means of the ball ramp device 3, 3 ' on the brake shoe holder 31, 31 ' and the brake shoe 4, 4 ' engaging therewith.

Each ball-ramp device 3, 3' mainly comprises an

expander piston

22, 23, an

actuation piston

17, 18 rotatable about an axis a with respect to the

expander piston

22, 23, and a plurality of balls 34. On their respective facing end faces, the first and

second actuation pistons

17, 22 and the second and

third expander pistons

18, 23 each have the same number of

lower recesses

32, 33 on the same circumferential circle, said

lower recesses

32, 33 being arranged in a regularly distributed manner in the circumferential direction. The depressions 32 in the

actuation pistons

17, 18 are each formed in a gradually flattened manner in a first circumferential direction, and the depressions 33 in the

expander pistons

22, 23 correspond to the depressions 32, but are flattened in an opposite second circumferential direction. A ball 34 is disposed between each of the

lower recesses

32 and 33. Due to the rotation of the

actuation pistons

17, 18 in the actuation direction relative to the

expander pistons

22, 23, the balls 34 roll into the flattened areas of the

depressions

32, 33 and push the piston pairs apart (or vice versa).

The two

expander pistons

22, 23 are secured against rotation relative to the housing 14 and are therefore only linearly movable along the axis a. In the embodiment shown, the fastening against rotation is ensured by supporting the respective brake shoe holder 31, 31 ' on the brake shoe 4, 4 ' by means of a transverse groove 36, 36 '. In this case, each brake shoe holder 31, 31 'is connected in a secured, non-rotating manner to the respective associated

expander piston

22, 23 by an outer sleeve 35, 35' which is bent inwards at the edges. In this case, each

expander piston

22, 23 is arranged within an outer sleeve 35, 35 ' in an axially spaced manner from the associated brake shoe holder 31, 31 ', with a spring element 37, 37 ' respectively preloaded therebetween. As a result, a limited linear movement in the axial direction is possible, and this ensures that the increase in clamping force when the drum contracts is limited by the compression of the spring element 37, in order to preclude damage to the brake.

The transmission of the required rotational movement of the ball-ramp device 3, 3' takes place by means of a first actuating piston 17 and a second actuating piston 18. For the purpose of uniform contact between the brake linings 5, 5' and the inner wall 7, two actuating

pistons

17, 18 are arranged in the drive sleeve 9 in an axially floating manner and in a manner secured against rotation by axial guidance.

The reconditioning device 26 essentially comprises a reconditioning piston 19 in the same force transmission path as the first actuating piston 17, and a locking sleeve 27 which is engaged with the reconditioning piston 19 and arranged in a manner secured against rotation relative to the second expander piston 28, but arranged in a manner allowing a limited degree of axial movement and under elastic preload against the reconditioning piston.

The separate readjustment piston 19 is screwed by means of a threaded portion 21 into a threaded hole 20 in the first actuation piston 17 as far as a stop position and is thus located in the force transmission path between the first actuation piston 17 and the second actuation piston 18. On its end face facing the second actuating piston 18, the readjusting piston 19 has an axially projecting, annular first sawtooth ramp 38 with a plurality of tooth ramps or notches which are inclined in one circumferential direction.

The locking sleeve 27 is arranged in such a way that it is substantially integrated into the second actuating piston 18. It has an axially projecting, annular second sawtooth ramp 39, which corresponds to the first sawtooth ramp 38 and likewise consists of a plurality of tooth ramps or notches inclined in the opposite circumferential direction.

A locking sleeve 27 is mounted on the rod 28 of the second expander piston 23 through a central hole in a manner allowing axial movement and in a manner secured against rotation relative to the housing 14. In the embodiment shown, a transverse pin 29 is provided in the rod 28 to prevent rotation, the locking sleeve 27 being supported on said pin 29 in both circumferential directions by means of an axially projecting slotted collar 42.

The locking sleeve 27 is pressed permanently with a slight force against a toothed ramp 38 of the readjustment piston 19 by a compression spring 30 supported on the second actuating piston 18. The sliding disc 43 reduces the friction and rotation of the compression spring 30 when the second actuation piston 18 rotates.

In the illustrated embodiment, the compression spring 30 is in the form of a wave spring. Other embodiments, such as coil spring or coil spring assemblies, are equally permissible within the present invention.

When the two actuating

pistons

17 and 18 are driven by the drive sleeve 9, the readjustment piston 19 rotates relative to the locking sleeve 27, which is not movable in the circumferential direction. In the process, the ramp surfaces of the readjustment piston 19 run up onto the ramp surfaces of the locking sleeve 27 during each actuation or braking operation and push them slightly into the second actuation piston 18, in contrast to the spring action of the compression spring 30. As the wear of the brake linings 5, 5' increases, the required stroke and the angle of rotation of the drive sleeve 9 and the readjustment piston 19 coupled thereto also increase. As soon as the angle exceeds the circumferential length of the ramp of the

sawtooth ramps

38, 39, the axial tooth between the locking sleeve 27 and the readjusting piston 19 jumps into the next recess. If the brake is released after the braking operation, the first actuating piston 17 rotates back with the drive sleeve 9 into the unactuated initial position. However, the readjustment piston 19 is prevented from rotating back by the rotationally fixed locking sleeve 27 and is therefore rotated out of the first actuating piston 17 by a corresponding amount. Thus, when the drum brake 1 is released, the brake is incrementally readjusted in a fully automatic stroke controlled manner.

In the following, an embodiment of a blocking device for use with a dilator unit according to fig. 2 is described.

In this regard, fig. 3a, 3b show details of the region of the dog clutch, which comprises the locking sleeve 27 and the readjusting piston 19. With a blocking space 50 therebetween. For this purpose, an annular undercut 51 is located in the end face of the readjustment piston 19, and a circular undercut 52, which is coaxial therewith, is located in the locking sleeve 27. In this case, the outer diameter of the annular depressed portion 51 is larger than the outer diameter of the circular depressed portion 52. The sawtooth slopes 38, 39 follow radially outside the undercut. The bottoms of the

lower recesses

51, 52 are parallel to and opposite each other. The blocking space 50 is delimited on one side by the bottom of the annular undercut 51 and on the other side by the opposite serrated bevel 39 on the locking sleeve 27.

A coil spring 53 made of bimetal is located in the annular lower recess 51. The depth of the annular lower recess corresponds to the width of the coil spring 53. One side of the coil spring 53 is located at the bottom of the annular undercut 51 so that its other side extends as far as the head end of the sawtooth ramp 39 on the locking sleeve 27. In this case, the coil spring 53 may be fastened to the center pin in the annular depressed portion 51.

Fig. 3a shows the unactuated brake in a cold state. The two saw tooth ramps 38, 39 engage each other so that the helical spring 53 extends into the circular lower recess 52. This is possible because its diameter in the cold state is smaller than the diameter of the circular undercut 52. As long as the brake does not overheat during a braking operation, the diameter of the helical spring 53 remains smaller than the diameter of the circular undercut 52, so that, as shown in fig. 3b, it does not fill the annular undercut 51 as far as its outer diameter, but the two

sawtooth ramps

38, 39 do not engage and fall back to the next locking step upon further rotation, so that a wear-related clearance correction can subsequently be carried out, as described in connection with fig. 2.

The situation is different when the brake heats up significantly. This is illustrated in fig. 3 c. When the two

sawtooth ramps

38, 39 are not engaged, i.e. the maximum pawl stroke has been performed, the annular spring expands into the blocking space 50 between the sawtooth ramp 39 on the locking sleeve 27 and the bottom edge of the annular undercut 51. Thus, even when they are rotated relative to each other through the step width, the

sawtooth ramps

38, 39 cannot enter into engagement in a new locking step. Conversely, when the brake is released, the

sawtooth ramps

38, 39 will first again occupy their old angular position and later engage there again when the helical spring 53 cools and contracts again.

However, since not every braking operation is associated with the development of heat, readjustment is not impeded during one of the subsequent braking operations, so that the lining wear thus accumulated up to now can be compensated for.

Instead of a coil spring, it is also possible to use a star-shaped element according to fig. 4a, 4b, which has a centre 55 from which, for example, four arms 56 with bimetal extend. In the cold state, the arms 56 are shortened (fig. 4a) and in the heated state they are extended (fig. 4b) so that their distal ends are located between the locking sleeve 27 and the readjustment piston in the blocking space 50, so that the

sawtooth ramps

38, 39 cannot assume the rotated locking position.

Fig. 5a shows an embodiment of the bimetal element in the form of two coaxially arranged

coil springs

60, 61 made of bimetal, which are arranged in a coaxial manner such that their mutually facing faces are concave in the cold state. Their edges in the barrier space 50 are thus close together and cannot fill the width of the barrier space 50. When the brake heats up (fig. 5b), the disc springs turn over so that their concave sides are now on the outside and their edges are spaced apart. As a result, they fill the width of the blocking space 50 and therefore the

sawtooth ramps

38, 39 cannot take up the rotated locking position, preventing readjustment.

In order to achieve a sufficiently large difference between the edge widths in the cold state and in the heated state even in the case of very small flip angles of the disk springs 60, 61, two (or more) disk spring pairs 65 can be arranged consecutively (one after the other), as shown in fig. 6, with a spacer ring 66 between them in each case.

List of reference numerals

1 drum brake

2 dilator unit

3-ROTATION-TRANSLATION DEVICE, IN PARTICULAR A BALL-SLOPE DEVICE

4 brake shoe

5 brake lining

6 brake drum

7 inner wall

8 drive unit

9 drive sleeve

10 external tooth

12 end part

13 end part

14 casing

15 rolling bearing (needle bearing)

16 fastening element

17 actuating piston

18 actuating piston

19 readjusting piston

20 screw hole

21 screw thread part

22 expander piston

23 expander piston

26 readjusting device

27 locking sleeve

28 rod

29 transverse pin

30 compression spring

31 brake shoe holder

32 lower concave part

33 lower concave part

34 ball

35 outer sleeve

36 transverse groove

37 spring element

38 saw tooth inclined plane

39 sawtooth slope

42 collar

43 sliding disk

50 blocking space

51 annular undercut

52 circular lower recess

53 helical spring

55 center

56 arm

60 coil spring

61 coil spring

62 coil spring pair

66 spacer ring

The A axis.

Claims

1. An expander unit (2) for a drum brake (1), comprising a housing (14) and two, first and second, brake shoe holders (31, 31 ') which are arranged in a rotationally fixed manner relative to the housing (14), can be linearly actuated along an axis (A) in an expansion direction (S, S') away from each other and in a release direction (L, L ') towards each other, respectively, and act on first and second brake shoes (4, 4') which are provided with brake linings (5, 5 '), respectively, with one or more rotation-translation conversion devices, wherein a readjustment device (26) for compensating an increased actuation stroke due to wear of the brake linings (5, 5') is arranged between the actuation pistons, the readjustment device (26) being designed such that it changes the spacing of the actuating pistons in at least one readjustment step when the actuating stroke has exceeded a set value, characterized in that a thermally activatable blocking device is provided which is designed to mechanically prevent the readjustment device from performing the readjustment step at a temperature above the set value.

2. The expander unit as claimed in claim 1, wherein the readjustment means (26) have a freewheel clutch comprising two pawls, wherein during idle rotation the pawls execute a relative stroke, and wherein one pawl is connected in a secure, non-rotating manner to the first brake shoe holder (31) and the other pawl is connected by a threaded shaft to the second actuation piston (18); and the blocking device is operatively arranged parallel to the dog clutch and thus keeps the dogs apart in the activated state.

3. Dilator unit according to claim 1, wherein the claws have on one of the respective end faces a saw tooth bevel (38, 39) extending circularly and engaging each other, wherein the length of the bevel on the circular arc defines the predetermined step width and the height of the bevel defines the maximum claw stroke.

4. A dilator unit according to claim 2 or 3, wherein the blocking means has a bimetallic element; and, between the jaws, a blocking space (50), said blocking space (50) being laterally delimited by the jaws, wherein the bimetal element is arranged such that it can expand into or in the blocking space at least when the maximum jaw travel has been reached.

5. An expander unit as claimed in claim 4, in which the bimetallic element has a helical spring (53) whose diameter varies as a function of temperature and which is arranged such that its outer edge enters the blocking space (50) when a temperature-dependent expansion occurs.

6. The dilator unit according to claim 4, wherein the bimetal element has at least one arm extending from the center, said arm lengthening depending on the temperature, and said arm is arranged such that the distal end of the arm enters into said blocking space (50) upon the occurrence of a temperature-dependent lengthening of the arm.

7. The expander unit as claimed in claim 6, wherein the bimetallic element has a plurality of arms, preferably arranged in a star shape.

8. An expander unit as claimed in claim 4, wherein the bimetal element has two coil springs (60, 61) arranged in opposite directions, one respective side of said two coil springs being convex or concave depending on the temperature, and the outer edges of said two coil springs being located in the blocking space (50).

9. The expander unit of claim 8, wherein at least two pairs of discs are provided.

10. The expander unit of claim 9, wherein the spacer ring is located between the pair of discs.

11. The expander unit as claimed in any one of claims 2 to 9, wherein the claw associated with the first brake shoe holder is in the form of a locking sleeve (27) fixedly connected to the first brake shoe holder (31); and the pawl coupled with the second actuating piston is in the form of a readjusting piston, wherein the locking sleeve (27) is secured against rotation relative to the second brake shoe holder (31'), is axially movable relative to the second actuating piston (18) over a limited range, and is arranged in an elastically preloaded manner against the readjusting piston (19).

12. The expander unit according to one or more of the preceding claims 1-11, wherein at least one rotation-translation transformation device is configured for linear movement of the shoe holder (31, 31'), which is achieved by:

a) ball-ramp device (3, 3 '), wherein the first ball-ramp device (3) has a first actuating piston (17) arranged to be rotatable about an axis (A), and optionally the second ball-ramp device (3') has a second actuating piston (18) arranged to be rotatable about an axis (A), and/or has a ball-ramp device

b) At least one or more nut-spindle drives, in particular with interposed rolling bodies, in particular with balls, and/or

c) Any hybrid configuration having the features of variants a) and/or b).

13. The expander unit as claimed in one or more of the preceding claims 1-12, characterized in that it is configured to be electromechanically drivable by means of an electromechanical actuator comprising an electric motor.

14. Expander unit as claimed in one or more of the preceding claims 1 to 13, characterized in that it is equipped indirectly or directly with an electrical load measuring device, for example cooperating with the load measuring device, in particular for applying the drum brake under electrical open-loop and/or closed-loop control.